This invention provides a process for recovering zein protein from gluten meal prepared from corn or other gluten bearing grains. The process of the invention is designed for implementation as an add-on module in existing wet milling alcohol production plants or as an integrated unit at new alcohol production facilities.
Zein is a hydrophobic protein found corn, millet, rice and other plants. Zein has many commercial uses including the manufacture of edible food packaging, edible films, biodegradable plastic resins, and tablet coating compounds. In U.S. corn wet milling facilities, zein is typically concentrated into a co-product fraction commercially referred to as corn gluten meal (CGM). CGM is commonly used as a protein source in animal food products without any attempt to recover the more valuable zein protein the CGM contains.
There are many known techniques for recovering zein as well as other natural ingredients such as oil, from corn. U.S. Pat. No. 4,716,218 to Chen et al. describes a process for producing grain oil, dehydrated alcohol, grain protein such as zein and starch utilizing ethanol extraction. The process for the production of grain oil and dehydrated alcohol by cracking the grain; drying the grain to a moisture content sufficiently low to enable the grain to dehydrate an ethanol solution to greater than 90% ethanol, while simultaneously extracting the grain oil from the dried grain with an ethanol solution of greater than 90% ethanol, and recovering the grain oil and dehydrated alcohol from the extractant. In a preferred embodiment, cracking the grain, drying the grain to a moisture content sufficiently low to dehydrate an ethanol solution of greater than 90% ethanol while simultaneously extracting oil from the dried grain with a first ethanol solution of greater than 90% ethanol, recovering oil and dehydrated alcohol from the first extractant, extracting grain protein from the residue of step with a second ethanol solution wherein the ethanol concentration is that which maximizes the protein solubility, recovering the protein from the second extractant, recovering starch from the residue of step.
U.S. Pat. No. 5,410,021 to Kampen describes and claims a process for recovering protein, protein isolate or starch from cereal grains such as corn that utilizes wet-attrition milling to break the protein-starch bonds while leaving the starch granulates intact. Kampen""s process includes recovering protein from cereal grains containing starch and protein bound into a matrix by the grinding said grains to a particle size appropriate for introduction to a wet attrition mill; defatting said grain; wet attrition milling particles of said grain to a size sufficiently small to break the bond between starch and protein, then extracting the broken bond protein from the starch with at least one solvent, then separately the resulting high liquid content portion containing the extracted protein from the resulting high solids content portion containing the starch, and then subjecting the high liquid content portion containing the extracted protein to continuous cross-flow microfiltration with inorganic membranes for isolating the protein constituent, concentrating the protein constituent into a dry power.
U.S. Pat. Nos. 5,254,673 and 5,580,959 to Cook disclose extraction of zein, zein bodies, glutelins or destarched corn gluten from corn gluten meal by enzymatic starch hydrolysis with an amylase, alkaline treatment, alcohol washing and alcohol extraction to yield a starch-free, deflavored and decolored zein. The method includes the steps of removing color and flavor impurities from the gluten by treating corn gluten with alkali to remove fatty acids and corn oils contained therein and then with an aqueous alcoholic solvent having a concentration which does not substantially extract zein, zein bodies and glutelins therefrom, thereafter changing the concentration of the alcoholic solvent to a concentration sufficient to separate the gluten into decolored and deflavored zein or zein bodies and glutelin fractions.
U.S. Pat. No. 4,486,353 to Matzuzaki et al. discloses a specific process of extracting vegetable oil and fats from oleaginous raw material such as corn gern by obtaining flakes having a moisture content of from 0.7 to 10 weight % from an oleaginous raw material, said flake being characterized by the absence of an impervious outer hull or coat; contacting said flakes with an ethanol solution containing not less than 90 weight % ethanol at a temperature in the range from 70xc2x0 C., to the boiling point of said ethanol solution, thereby obtaining a miscella, cooling said miscella, thereby obtaining vegetable oil or fat or both, and a separate defatted miscella; drying said defatted miscella with a molecular sieve material having a pore size from 3 xc3x85 to 4 xc3x85, thereby obtaining a second ethanol solution wherein said second ethanol solution contains less than 7 weight % water; and using said second ethanol solution as the ethanol solution of said contacting step in a second extraction.
U.S. Pat. No. 5,773,076 to Liaw et al. is directed to a wet milling process in which gluten is recovered from steep water by membrane filtration and is then incorporated into a corn gluten meal product. The process of recovering insoluble gluten protein from steep water in a corn wet milling process includes steeping corn kernels in an aqueous solution that comprises gluten wash water, thereby producing steep water which contains insoluble gluten protein; membrane filtration of the steep water, thereby producing a retentate which has a higher concentration of the insoluble gluten protein than the original steep water; reducing the water content of the retentate; and incorporating the remaining retentate into a corn gluten meal product.
U.S. Pat. No. 5,342,923 to Takahashi et al. describes a process for refining zein with a high purity acetone solution by dispersing a solution containing crude zein into a solution comprising acetone in which said zein is insoluble; thereby precipitating a zein component as porous solids; separating said porous solids; and drying said solids. U.S. Pat. No. 5,510,463 to Takahaski et al. discloses a process for producing zein wherein zein and pigment components are extracted from a corn gluten meal that has been treated with a C5-C9 hydrocarbon solvent. The zein is extracted by subjecting the treated corn gluten meal with a solvent having 91-96% by volume ethanol. The zein and the pigment components are then separated from the extract solution. Oil and fat components and pigment components may be extracted prior to the zein extraction steps.
U.S. Pat. No. 5,367,055 to Takahashi et al. discloses a process for treating a zein containing material to decrease inherent color and smell and to obtain zein by contacting the material with an aqueous acetone solution having an acetone solution which xe2x80x9ccauses almost no dissolutionxe2x80x9d of the zein compound. The process includes the steps of contacting the zein-containing material with (1) a 80-100% (V/V) acetone solution at a temperature of 25-60xc2x0 C., or (2) a 70-80% (V/V) acetone solution at a temperature of 25-40xc2x0 C., and separating the resulting solid from the solution.
U.S. Pat. No. 4,624,805 to Lawhon describes a process for recovering food grade protein from agricultural commodities, e.g., corn, prior to alcohol production. The process includes the steps of obtaining a suitable agricultural commodity in a form suitable for extraction of protein; extracting protein from said agricultural commodity with an alkali solution which forms a dispersion with said agricultural commodity; separating the dispersion into a solids fraction and a liquids fractions, said liquids fraction containing extracted protein; removing the protein from said liquids fractions by ultrafiltration using a membrane having a molecular weight cutoff between about 10,000 and about 30,000 daltons; and utilizing said solids fraction for alcohol production.
The present invention provides an economical process for extracting zein from gluten prepared from corn or other grains at a wet milling facility that produces ethanol. The process incorporates a water washing step, preferably using counter current techniques, to remove water-soluble components from wet or dry gluten. The water washing step is immediately followed by extraction with an aqueous ethanol solvent to remove the zein protein fraction of the gluten. The insoluble gluten components such as starch and cellulose are then separated from the solution, e.g. by centrifugation or filtration. The starch-bearing solids may then be hydrolyzed to simple sugars by acid conversion technology and used as feed for an existing fermentation system.
The alcoholic zein solution is treated with activated carbon or another adsorbent to remove at least one of color, odor, and other undesirable components from the zein. When activated carbon is used as the adsorbent, the resulting zein solution is clear. This solution is then preferably filtered and dried, e.g, by spray drying to obtain a high-purity zein product that is suitable for use, e.g. in producing edible films and biodegradable plastic resins. The filtered zein solution can also be directly incorporated in the manufacture of other products without drying, e.g, for direct use in a process for preparing biodegradable polymers.